Compared with lap-top PCs, cellular phones, and other similar devices, vehicular secondary batteries and large-scale power storage systems are required to rigorously be safely controlled. A method for estimating a deterioration state of a lithium ion secondary battery by determining whether lithium is deposited is widely known. In PTL 1, an amount of change (dV/dt) in battery voltage V that gradually rises per time t through constant current charging is detected, and a minimum value of the amount of change (dV/dt) in battery voltage V per time t is calculated to determine whether lithium is deposited.
In PTL 2, an OCV and an SOC of a lithium ion secondary battery of a vehicle that has moved a predetermined travel distance are calculated, and these values are compared with an OCV and an SOC at a time when the lithium ion secondary battery has not yet been used to determine whether lithium is deposited.